Layer-by-layer assembled magnetic bimetallic metal-organic framework composite for global phosphopeptide enrichment

The highly selective enrichment of phosphopeptides is vital for the research of phosphorylated proteomics. Herein, a magnetic bimetallic metal-organic framework (MOF) with Zr-O and Ti-O clusters (denoted as Fe 3 O 4 @SiO 2 @(Zr-Ti-PTA) 15 ) has been fabricated using a layer-by-layer assembly approach via the coordination of metal ions with carboxyl groups. The composite has large specific surface area (135.84 m 2  g −1 ) and superparamagnetism (62.03 emu g −1 ). Compared with single-metal cluster MOF, the Fe 3 O 4 @SiO 2 @(Zr-Ti-PTA) 15 showed higher binding capacity (100 mg g −1 ), enhanced affinity, better selectivity (n β-casein : n BSA  = 1 : 2000) and sensitivity (0.3 fmol/μL) towards phosphopeptides due to the combination of the dual metal clusters. Furthermore, the Fe 3 O 4 @SiO 2 @ (Zr-Ti-PTA) 15 was successfully applied to extracting phosphopeptides from non-fat milk tryptic digest, and 10 mono-phosphopeptides and 22 multi-phosphopeptides were captured. As a result, 1294 phosphopeptides (476 multi-phosphopeptides and 818 mono-phosphopeptides) were selectively extracted and detected from tryptic digest of rat brain extract, indicating its great application potential in phosphorylated proteomics research.